Iron pyridine-2-thiolate complexes: Interconversion of [Fe0(CO)4(SC5H4N)]-, cis-[FeII(CO)2(SC5H4N)2], and [FeII(SC5H4N)3]-

Article abstract of DOI:10.1021/om971004o

The reaction of bis(2-pyridyl) disulfide with [HFe(CO)₄]^- affords [Fe(CO)₄(SC₅H₄N)]^-, in which the pyridine-2-thiolate ligand is bound in a monodentate (S-bonded) mode. Oxidative addition of bis(2-pyridyl) disulfide to [Fe(CO)₄(SC₅H₄N)]^- and concomitant displacement of [SC₅H₄N]^- leads to the neutral monomeric compound cis-[Fe(CO)₂(SC₅H₄N)₂]. In the presence of [SC₅H₄N]^- in CH₃CN at 60°C, cis-[Fe(CO)₂(SC₅H₄N)₂] undergoes facile conversion to d⁶ Fe(II) high-spin [Fe(SC₅H₄N)₃]^-. Reduction of cis-[Fe(CO)₂(SC₅H₄N)₂] and [Fe(SC₅H₄N)₃]^- under CO at room temperature with [BH₄]^-/[Nα][benzophenone] affords the monodentate (S-bonded) complex [Fe(CO)₄(SC₅H₄N)]^-. The results are consistent with sulfur-donor atom stabilization of the lower oxidation states of iron, while the S,N-chelating pyridine-2-thiolate ligand enhances the stability of iron in the higher oxidation state.

Full text of DOI:10.1021/om971004o

2370
Organometallics 1998, 17, 2370-2372
Ir on P yr id in e-2-th iola te Com p lexes: In ter con ver sion of
[F e0(CO)4(SC5H4N)]-, cis-[F eII(CO)2(SC5H4N)2], a n d
[F eII(SC5H4N)3]-
Wen-Feng Liaw,*,† Chien-Hong Chen,† Gene-Hsiang Lee,‡ and Shie-Ming Peng§
Department of Chemistry, National Changhua University of Education,
Changhua 50058, Taiwan, and Instrumentation Center and Department of Chemistry,
National Taiwan University, Taipei 10764, Taiwan
Received November 14, 1997
Summary: The reaction of bis(2-pyridyl) disulfide with
[HFe(CO)4]- affords [Fe(CO)4(SC5H4N)]-, in which the
pyridine-2-thiolate ligand is bound in a monodentate (S-
bonded) mode. Oxidative addition of bis(2-pyridyl)
disulfide to [Fe(CO)4(SC5H4N)]- and concomitant dis-
placement of [SC5H4N]- leads to the neutral monomeric
compound cis-[Fe(CO)2(SC5H4N)2]. In the presence of
[SC5H4N]- in CH3CN at 60 °C, cis-[Fe(CO)2(SC5H4N)2]
undergoes facile conversion to d6 Fe(II) high-spin
[Fe(SC5H4N)3]-. Reduction of cis-[Fe(CO)2(SC5H4N)2]
and [Fe(SC5H4N)3]- under CO at room temperature with
[BH4]-/ [Na][benzophenone] affords the monodentate (S-
bonded) complex [Fe(CO)4(SC5H4N)]-. The results are
consistent with sulfur-donor atom stabilization of the
lower oxidation states of iron, while the S,N-chelating
pyridine-2-thiolate ligand enhances the stability of iron
in the higher oxidation state.
Ph, alkyl) to anionic metal carbonyl fragments.5b-e In
this work, we report a study of the interconversion of
the pyridine-2-thiolate complexes [Fe0(CO)4(SC5H4N)]-,
cis-[FeII(CO)2(SC5H4N)2], and [FeII(SC5H4N)3]- (Scheme
1).
Resu lts a n d Discu ssion
As illustrated in Scheme 1a, the reaction of bis(2-
pyridyl) disulfide with the anionic iron hydride
[HFe(CO)4]- leads to cleavage of the sulfur-sulfur bond
and concomitant addition of the pyridine-2-thiolate to
the iron-carbonyl fragment to yield [Fe0(CO)4(SC5H4N)]-,
with liberation of HSC5H4N.6 The thermally unstable
product, monodentate (S-bonded) [Fe0(CO)4(SC5H4N)]-,
was isolated as an oily compound. Treatment of 1 equiv
of [Fe(CO)4(SC5H4N)]- with bis(2-pyridyl) disulfide in
THF led to the formation of the neutral cis-[Fe(CO)2-
(SC5H4N)2] and elimination of [PPN][SC5H4N]. The
anionic SC5H4N- ligands in cis-[Fe(CO)2(SC5H4N)2] bind
to the metal in a bidentate manner, forming four-
membered chelate rings (Scheme 1b,c). The proposed
mechanism, shown in Scheme 1b,c, involves oxidative
addition of bis(2-pyridyl) disulfide to the anionic
[Fe(CO)4(SC5H4N)]-,5b,c,7a-c possibly via the intermedi-
ate fac-[FeII(CO)3(SC5H4N)3]-. (In a similar fashion, the
reaction of [HFe(CO)4]- with 2 equiv of (S(C4H3S))2 in
THF at ambient temperature leads to a thermally stable
crystalline solid fac-[FeII(CO)3(SC4H3S)3]- characterized
by X-ray crystallography.7d) Subsequent elimination of
SC5H4N- and concomitant dissociation of CO and
coordination of the nitrogen atom of the SC5H4N-
ligands to the Fe(II) result in formation of cis-[FeII(CO)2-
In tr od u ction
Metal pyridine-2-thiolate complexes have been stud-
ied because of their structural diversity,1 important
biological roles,2 and potential application as precursors
for metal-sulfide materials.3
We previously reported investigations into the bio-
mimetic nickel-site structures of [NiFeSe] hydrogenase
(nickel is ligated to one Se atom, one to two S/Cl atoms,
and three to four N/O atoms)4 and CO dehydrogenase5a
and the oxidative addition of RE-ER (E ) Te, Se; R )
† National Changhua University of Education.
‡ Instrumentation Center, National Taiwan University.
§ Department of Chemistry, National Taiwan University.
(1) (a) Rosenfield, S. G.; Swedberg, S. A.; Arora, S. K.; Mascharak,
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Kinoshita, I.; Ooi, S. Inorg. Chem. 1990, 29, 4005. (c) Mura, P.; Olby,
B. G.; Robinson, S. D. J . Chem. Soc., Dalton Trans. 1985, 2101. (d)
Santra, B. K.; Menon, M.; Pal, C. K.; Lahiri, G. K. J . Chem. Soc., Dalton
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V.; LeGall, J .; Moura, J . J . G.; Peck, H. D., J r. Proc. Natl. Acad. Sci.
U.S.A. 1989, 86, 147.
(5) (a) Liaw, W.-F.; Horng, Y.-C.; Ou, D.-S.; Ching, C.-Y.; Lee, G.-
H.; Peng, S.-M. J . Am. Chem. Soc. 1997, 119, 9299. (b) Liaw, W.-F.;
Chuang, C.-Y.; Lee, W.-Z.; Lee, C.-K.; Lee, G.-H.; Peng, S.-M. Inorg.
Chem. 1996, 35, 2530. (c) Liaw, W.-F.; Chiang, M.-H.; Liu, C.-J .; Harn,
P. J .; Liu, L.-K. Inorg. Chem. 1993, 32, 1536. (d) Liaw, W.-F.; Lee,
W.-Z.; Wang, C.-Y.; Lee, G.-H.; Peng, S.-M. Inorg. Chem. 1997, 36,
1253. (e) Liaw, W.-F.; Ou, D.-S.; Li, Y.-S.; Lee, W.-Z.; Chuang, C.-Y.;
Lee, Y.-P.; Lee, G.-H.; Peng, S.-M. Inorg. Chem. 1995, 34, 3747.
(6) (a) Liaw, W.-F.; Kim, C.; Darensbourg, M. Y.; Rheingold, A. L.
J . Am. Chem. Soc. 1989, 111, 3591. (b) Darensbourg, M. Y.; Liaw, W.-
F.; Riordan, C. G. J . Am. Chem. Soc. 1989, 111, 8051.
(7) (a) Liaw, W.-F.; Lai, C.-H.; Chiang, M.-H.; Lee, C.-K.; Lee, G.-
H.; Peng, S.-M. J . Chem. Soc., Dalton Trans. 1993, 2421. (b) Liaw,
W.-F.; Lai, C.-H.; Chiang, M.-H.; Hsieh, C.-K.; Lee, G.-H.; Peng, S.-M.
J . Chin. Chem. Soc. (Taipei) 1993, 40, 437. (c) Liaw, W.-F.; Ou, D.-S.;
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S0276-7333(97)01004-2 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/26/1998

Notes
Organometallics, Vol. 17, No. 11, 1998 2371
Sch em e 1
F igu r e 1. ORTEP drawing of one of two crystallographi-
cally independent molecules in cis-[Fe(CO)2(SC5H4N)2].
The X-ray crystal structure of cis-[Fe(CO)2(SC5H4N)2]
(Figure 1) consists of two crystallographically indepen-
dent molecules. The average Fe-S distance of 2.325(3)
Å is significantly shorter than that in high-spin d6 Fe-
(II) [Fe(SC5H4N)3]- (average distance 2.575(1) Å).1a The
bond angles at the Fe center are considerably distorted
from the idealized octahedral limits due to the presence
of two four-membered N,S-chelate rings, a characteristic
most apparent in the internal chelate angles, S-Fe-
N, of 71.1(2) and 71.0(2)°. This angle is larger than the
S-Fe(II)-N bond angle (average 66.0(2)°) observed in
[Fe(SC5H4N)3]-.1a The two carbonyl groups are disposed
in a cis arrangement and are trans to the nitrogen
atoms.
(SC5H4N)2]. This complex is soluble and stable in THF/
hexane solution. The IR spectrum shows two strong CO
stretching bands, which supports a cis orientation of two
CO ligands. The 1H and 13C NMR spectra show the
expected signals (1H NMR (CD3COCD3) δ 6.83 (m), 6.97
(m), 7.60 (m), 8.28 (m) ppm; 13C NMR (CD3COCD3) δ
119.2, 126.1, 138.4, 147.2, 179.9 ppm) for the [SC5H4N]-
ligands in a diamagnetic d6 Fe(II) species.
When allowed to stir in the presence of 1 equiv of the
[SC5H4N]- ligand for 4 h in CH3CN at 60 °C, cis-[Fe-
(CO)2(SC5H4N)2] loses the carbonyl ligands to form the
known d6 high-spin tris-chelate [Fe(SC5H4N)3]- (Scheme
1d).1a Alternatively, complete conversion of [Fe(CO)4-
(SC5H4N)]- to [Fe(SC5H4N)3]- was observed when 1
equiv of bis(2-pyridyl) disulfide was added to [Fe-
(CO)4(SC5H4N)]- and the solution was allowed to stir
for 4 h in CH3CN at 60 °C. The results suggest that
the S,N-chelating pyridine-2-thiolate ligand enhances
the stability of iron complexes in higher oxidation states.
In comparison, the carbon monoxide atmosphere does
not promote the formation of cis-[Fe(CO)2(SC5H4N)2]
when the [Fe(SC5H4N)3]-/CH3CN solution is exposed to
1 atm of CO at room temperature.
In summary, the complexes [Fe0(CO)4(SC5H4N)]-, cis-
[FeII(CO)2(SC5H4N)2], and [FeII(SC5H4N)3]- are chemi-
cally interconvertible. The Fe(0) complex contains a
monodentate [SC5H4N]- ligand, which binds as an S,N-
bidentate ligand in the Fe(II) complexes.
Exp er im en ta l Section
Manipulations, transfers, and reactions of samples were
conducted under nitrogen according to standard Schlenk
techniques or in a glovebox (Ar gas). Solvents were distilled
under nitrogen from appropriate drying agents (diethyl ether
from CaH2; acetonitrile from CaH2/P2O5; hexane and THF from
Na/benzophenone) and stored in dried, N2-filled flasks over 4
Å molecular sieves. A nitrogen purge was used on these
solvents before use, and transfers to reaction vessels were via
stainless steel cannula under N2 at a positive pressure. The
reagents bis(2-pyridyl) disulfide, iron pentacarbonyl, bis-
(triphenylphosphoranylidene)ammonium chloride ([PPN][Cl]),
and tetraethylammonium hydroxide (Aldrich) were used as
received. Infrared spectra were recorded on a spectrometer
(Bio-Rad FTS-185 FTIR) with sealed solution cells (0.1 mm)
and KBr windows. 1H and 13C chemical shifts are relative to
tetramethylsilane. UV-visible spectra were recorded on a
GBC 918 spectrophotometer. Analyses of carbon, hydrogen,
and nitrogen were obtained with a CHN analyzer (Heraeus).
P r ep a r a tion of [P P N][F e(CO)4(SC5H4N)]. [PPN][HFe-
(CO)4] (1 mmol, 0.708 g) dissolved in THF (3 mL) was stirred
under N2,9 and a solution of bis(2-pyridyl) disulfide (1 mmol,
0.220 g) in THF (7 mL) was added dropwise by cannula under
positive N2 gas at room temperature. After an additional 5
The ring-opened complex [Fe(CO)4(SC5H4N)]- was
obtained upon chemical reduction of cis-[Fe(CO)2-
(SC5H4N)2] and [Fe(SC5H4N)3]- with [BH4]- and [Na]-
[benzophenone] under CO in THF at room temperature,
respectively (Scheme 1e, f).8 Apparently, the metal-
centered reduction of cis-[FeII(CO)2(SC5H4N)2] and
[FeII(SC5H4N)3]- labilizes the [SC5H4N]- chelating
ligands and results in the formation of the pentacoor-
dinate species [Fe0(CO)4(SC5H4N)]-. The loss of the
S,N-chelating pyridine-2-thiolate ligands from the Fe-
(0) center may be due to the electron density at the iron-
(0) center. The ligand [SC5H4N]- was not observed to
undergo reduction, and consequently, the reduction
process is assigned to the iron(II)-iron(0) couple.
(8) (a) Marganian, C. A.; Vazir, H.; Baidya, N.; Olmstead, M. M.;
Mascharak, P. K. J . Am. Chem. Soc. 1995, 117, 1584. (b) Baidya, N.;
Olmstead, M. M.; Whitehead, J . P.; Bagyinka, C.; Maroney, M. J .;
Mascharak, P. K. Inorg. Chem. 1992, 31, 3612.
(9) Smith, M. B.; Bau, R. J . Am. Chem. Soc. 1973, 95, 2388.

2372 Organometallics, Vol. 17, No. 11, 1998
Notes
Ta ble 1. Cr ysta llogr a p h ic Da ta for
min of stirring, the volume of the solution was reduced to 3
mL and the orange oily product precipitated by addition of
hexane (15 mL). The thermally unstable product was isolated
by removing the solvent (since decomposition occurred after
prolonged vacuum, the percent yield of the oily [PPN][Fe(CO)4-
(SC5H4N)] was difficult to determine.). IR (νCO) (THF): 2017
cis-[F e(CO)2(SC5H4N)2]
empirical
C12H8O2N2FeS2
332.17
fw
cryst syst
space group
λ(Mo KR), Å
a, Å
monoclinic
P21/c
0.7107
12.688(5)
16.083(3)
13.725(5)
91.18(3)
2800(2)
8
w, 1912 vs cm-1 1H NMR (CD3CN): δ 8.19 (br), 7.33 (m), 7.16
.
(br) ppm (SC5H4N). 13C NMR (CD3CN): δ 218.94 (s) ppm (CO),
171.16, 148.56, 135.56, 125.51, 116.56 ppm (SC5H4N).
b, Å
c, Å
P r ep a r a tion of cis-[F e(CO)2(SC5H4N)2]. [PPN][HFe-
(CO)4] (1 mmol, 0.708 g) was added to bis(2-pyridyl) disulfide
(2 mmol, 0.440 g) in THF (10 mL) at ambient temperature.
After 12 h of stirring at room temperature, the solvent was
removed at reduced pressure. The residue was redissolved in
20 mL of THF/hexane, and the red solution was filtered to
remove [PPN][SC5H4N]. The filtrate was stored at - 15 °C
for 4 weeks to induce precipitation of dark red crystals of cis-
[Fe(CO)2(SC5H4N)2]. The yield was 0.221 g (66.6%). IR (νCO):
â, deg
V, Å3
Z
F
calcd, g cm-3
1.576
µ, cm-1
13.586
1349
F(000)
no. of measd reflcs
3657
no. of obsd reflcs (I > 2σ(I))
no. of refined params
2190
343 (2190 out of 3657 reflcs)
T, °C
25
0.053
0.055
1
2040 vs, 1989 s cm-1 (THF); 2047 s, 2000 s cm-1 (hexane). H
Ra
NMR (CD3COCD3): δ 6.83 (m), 6.97 (m), 7.60 (m), 8.28 (m)
Rwb
ppm (SC5H4N). 13C NMR (CD3COCD3): δ 213.8 (CO), 119.2,
a
b
2 1/2
R ) ∑|(Fo - Fc)|/∑Fo. R ) [∑w(Fo - Fc)2/∑wFo
] .
126.1, 138.4, 147.2, 179.9. Absorption spectrum (THF) [λmax
,
nm (ꢀ, M-1 cm-1)]: 517 (166), 346 (3922), 306 (13 885). Anal.
Calcd for C12H8O2N2S2Fe: N, 8.43; C, 43.39; H, 2.43. Found:
N, 8.51; C, 43.58; H, 2.50.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for cis-[F e(CO)2(SC5H4N)2]
S(1a)-Fe(a)
N(1a)-Fe(a)
C(1a)-Fe(a)
S(1a)-C(3a)
2.322(3)
2.004(7)
1.761(9)
1.730(9)
S(2a)-Fe(a)
N(2a)-Fe(a)
C(2a)-Fe(a)
S(2a)-C(8a)
2.328(3)
1.986(7)
1.764(10)
1.711(9)
P r ep a r a tion of [P P N][F e(SC5H4N)3]. A solution contain-
ing cis-[Fe(CO)2(SC5H4N)2] (0.3 mmol, 0.099 g) and [PPN]-
[SC5H4N] (0.3 mmol, 0.195 g) in 15 mL of CH3CN was heated
at 60 °C under nitrogen for 4 h. When the solution cooled to
room temperature, the volume of the solution was reduced to
3 mL under vacuum and diethyl ether (20 mL) was added.
The known orange [PPN][Fe(SC5H4N)3] was isolated by re-
moving the solvent and recrystallized from acetonitrile/diethyl
ether.1a The yield was 0.190 g (68.6%). 1H NMR (CD3CN): δ
98.10 (br), 78.25 (s), 58.45 (s), 7.14 (s) ppm.1a
S(1a)-Fe(a)-S(2a) 163.06(11) Fe(a)-S(1a)-C(3a)
78.5(3)
78.3(7)
S(1a)-Fe(a)-N(1a)
S(1a)-Fe(a)-N(2a)
S(1a)-Fe(a)-C(1a)
S(2a)-Fe(a)-N(2a)
71.14(19) Fe(a)-S(2a)-C(8a)
96.19(20) Fe(a)-N(1a)-C(3a) 100.2(5)
94.1(11) Fe(a)-N(1a)-C(7a) 139.9(6)
70.96(20) Fe(a)-N(2a)-C(8a) 100.4(5)
N(1a)-Fe(a)-C(2a) 166.3(3)
N(2a)-Fe(a)-C(1a) 168.3(4)
Fe(a)-N(2a)-C(12a) 138.3(6)
C(1a)-Fe(a)-C(2a) 91.6(4)
Rea ction of [P P N][BH4] w ith cis-[F e(CO)2(SC5H4N)2]
(a n d [Na ][ben zop h en on e] w ith [P P N][F e(SC5H4N)3]). A
solution containing 0.167 g (0.5 mmol) of cis-[Fe(CO)2-
(SC5H4N)2] and 0.553 g (1 mmol) of [PPN][BH4] in THF (15
mL) was stirred under CO atmosphere for 8 h at room
temperature. The IR spectrum (νCO (THF): 1912 vs, 2017 w
cm-1) was identical to that of [PPN][Fe(CO)4(SC5H4N)].
Cr ysta llogr a p h y. The crystal data are summarized in
Table 1. Due to air sensitivity, the crystal of Fe(CO)2(SC5H4N)2
(ca. 0.20 × 0.40 × 0.40 mm) was mounted on a glass fiber and
quickly coated in epoxy resin. The unit-cell parameters were
obtained from 25 reflections with 2θ between 17.64 and 25.50°.
Diffraction measurements were carried out on a Nonius CAD
4 diffractometer with graphite-monochromated Mo KR radia-
tion employing the θ/2θ scan mode.10 A æ scan absorption
correction was made. Structural determinations were made
using the NRCC-SDP-VAX package of programs.11,12 Selected
bond distances and angles are listed in Table 2.
Ack n ow led gm en t. We thank the National Science
Council (Taiwan) for support of this work.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and experimental conditions for the X-ray studies, atomic
coordinates and Beq values, anisotropic thermal parameters,
and bond lengths and angles for Fe(CO)2(SC5H4N)2 (5 pages).
Ordering information is given on any current masthead page.
OM971004O
(11) Gabe, E. J .; LePage, Y.; Charland, J . P.; Lee, F. L.; White, P.
S. J . Appl. Crystallogr. 1989, 22, 384.
(12) Atomic scattering factors were obtained from the following:
International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(10) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.